1. Field of the Invention
The present invention relates to a plasma deposition method and apparatus for depositing a thin film of various materials over the surface of a substrate in the case of fabrication of electronic devices such as semiconductor integrated circuits and more particularly to a plasma deposition method and apparatus for forming a high quality thin film of metals or metal compounds at a low temperature by utilizing plasma.
2. Description of the Prior Art
Apparatus for depositing thin films by utilizing plasma may generally be classified into a sputtering apparatus and a plasma CVD apparatus. The sputtering apparatus is mainly used to deposit films of metals or metal compounds, while the plasma CVD apparatus is mainly used to deposit a thin film of a material including silicon such as SiO.sub.2, Si.sub.3 N.sub.4, Si or the like.
As far as a way of supplying a raw materials, the sputtering device uses a target of a solid material which is subjected to bombardment of ions so that sputtered atoms ejected from the solid target are deposited over the surface of a substrate on which a film is to be formed. In the plasma CVD apparatus, raw materials such as SiH.sub.4, N.sub.2 or O.sub.2 are supplied in the form of a gas to be decomposed and reacted so as to form an Si.sub.3 N.sub.4 or SiO.sub.2 film over the surface of a substrate.
According to a conventional high-frequency discharge plasma CVD process, there are disadvantages in that a specimen substrate must be heated at 250.degree.-400.degree. C. and that a quality of a film such as density of an Si.sub.3 N.sub.4 film is not satisfactory.
In U.S. Pat. No. 4,401,054, there is a disclosure of a plasma deposition apparatus in which plasma is produced by utilizing a microwave discharge using electron cyclotron resonance (ECR) and the plasma is extracted toward a specimen table by means of a diverging magnetic field so that an ion bombardment occurs with suitable energies. According to this process, a dense and high quality silicon film such as Si.sub.3 N.sub.4 comparable with that obtained by a high temperature CVD method can be obtained at a low temperature without heating the substrate.
If, however, it is desired to deposita film of a metal or a metal compound there is no suitable gas available. In the case of forming a film of silicon, SiH.sub.4 gas can not be used, and the compounds which can be supplied in the form of gas are limited to halogen compounds such as flourides, chlorides or bromides. In order to supply such halogen compounds to the apparatus, a special gas introduction system as well as heating are required. In addition, the decomposition by plasma is difficult or unstable. Therefore, there is a disadvantage that it is difficult to obtain a high quality film.
According to the conventional sputtering method, atoms which impinge against a specimen substrate are not ionized in order to promote a reaction of forming a film and their energies are not controlled so that there is a disadvantage that a high quality film cannot be obtained at a low temperature and the adhesion of the film to the substrate is not satisfactory.